1. Field of the Invention
The present invention relates to a glass-ceramic composition containing a glass component sinterable at low temperature, a glass-ceramic sintered body prepared by firing the glass-ceramic composition, and a monolithic ceramic electronic component including the glass-ceramic sintered body.
2. Description of the Related Art
In recent years, multifunctional electronic components have been used in order to manufacture compact electronic devices. Examples of such multifunctional electronic components include multilayer ceramic modules.
The multilayer ceramic modules each include a multilayer ceramic substrate. The multilayer ceramic substrate includes wiring conductors, arranged therein, for electrical connection and/or for forming passive elements such as capacitors and inductors. The multilayer ceramic substrate has various electronic components mounted thereon.
The multilayer ceramic modules are small-sized and multifunctional. Hence, the multilayer ceramic modules are useful in manufacturing compact electronic devices.
There are increasing demands for compact electronic devices operating at high frequencies. Therefore, multilayer ceramic modules operating at high frequencies need to include a multilayer ceramic substrate with good high-frequency properties. In particular, insulating ceramic sintered bodies for forming insulating ceramic layers included in this multilayer ceramic module need to have good high-frequency properties.
An insulating ceramic composition for forming the insulating ceramic sintered bodies meeting such requirements is disclosed in Japanese Unexamined Patent Application Publication No. 2000-344571 (hereinafter referred to as Patent Document 1). The insulating ceramic composition disclosed in Patent Document 1 contains three components: forsterite, calcium titanate, and spinel. The insulating ceramic composition has a Qf value of about 38,000 GHz or more and a temperature coefficient of dielectric constant of about −80 to 40 ppm/° C. when the ratio of the components is within a preferable range. The Qf value is determined by dividing the frequency (GHz) by the dielectric loss (tan σ).
The procedure for preparing those multilayer ceramic substrates included in that multilayer ceramic module includes a firing step. During firing step, the wiring conductors arranged in that multilayer ceramic module are also fired.
In order to allow that multilayer ceramic module to operate at high frequencies with no problems, the wiring conductors need to have low electrical resistance. Therefore, the wiring conductors need to be made of a metal, such as copper or silver, which has a low electrical resistance.
However, such a metal has a low melting point. Hence, in order to prepare the multilayer ceramic substrate by firing an insulating ceramic composition for forming the multilayer ceramic substrate together with the wiring conductors, the insulating ceramic composition needs to be sintered at low temperature, for example, about 1,000° C. or less.
Patent Document 1 discloses that the temperature of firing that insulating ceramic composition is about 1,140° C. to 1,600° C. Hence, that insulating ceramic composition cannot be sintered at about 1,000° C. or less.
In order to use that multilayer ceramic substrate for high-frequency applications and in order to densely arrange the wiring conductors, the insulating ceramic layers need to have a low dielectric constant. Patent Document 1 does not disclose the dielectric constant of an insulating ceramic sintered body prepared by sintering that insulating ceramic composition.
PCT Publication No. WO 2005/082806 (hereinafter referred to as Patent Document 2) discloses a glass-ceramic composition that can be sintered at about 1,000° C. or less. The glass-ceramic composition is useful in manufacturing a sintered body having a low dielectric constant and good high-frequency properties. The temperature coefficient of resonant frequency of the sintered body can be controlled so as to be small and the Qf value thereof can be controlled so as to be large.
In particular, the glass-ceramic composition disclosed in Patent Document 2 contains first ceramic particles principally containing forsterite; second ceramic particles principally containing at least one selected from the group consisting of calcium titanate, strontium titanate, and titanium oxide; and particles made of borosilicate glass. The borosilicate glass contains about 3% to 15% lithium in the form of Li2O, about 30% to 50% magnesium in the form of MgO, about 15% to 30% boron in the form of B2O3, about 10% to 35% silicon in the form of SiO2, about 6% to 20% zinc in the form of ZnO, and about 0% to 15% aluminum in the form of Al2O3 on a weight basis.
In recent monolithic ceramic electronic components, the ceramic layers for forming elements included in the components need to have a small thickness although the components are increasingly being used to process high-voltage signals. Therefore, a material for forming the ceramic layers needs to have higher electrical insulation reliability.